A person who is a member of the Church of Jesus Christ of Latter-Day Saints, but seldom or never practices their religion. Unlike ex-Mormons or anti-Mormons, Jack Mormons usually support the goals and beliefs of the church and maintain friendships with practicing Mormons, but for reasons of their own choose not to attend church services and activities. Jack Mormons may also indulge in activities discouraged by the church, such as drinking alcohol, smoking, and premarital sex.

Jack Mormon equivalents in other religions are "Christmas and Easter Christians" and "Yom Kippur Jews".
Although Tim was a mormon, he did not go to church on Sundays, and enjoyed drinking beer with his friends on weekends. Because of this, his buddies referred to him as a Jack Mormon.
by You Can't Kill the Metal April 5, 2006
A person who was subjected to the Church of Jesus Christ and Latter Day Saints at an early age. After smelling the Bull-Shit, then wised up and joined the rest of the sane world. Also see: A man who choses not to marry more than one woman at a time, or live on a compound.
"That Bill Bratsky used to be Morman, now the son of a bitch is on welfare and drinks all my beer! God Damn jack mormon!"
by Ryan from Zion August 13, 2006
A person who is a member of the Church of Jesus Christ of Latter Day Saints (Mormon), but doesn't follow their religion. They might get drunk and participate in pre-marital sex. This phrase traces its origins to high schools in Las Vegas. Antonym: molly mormon
1: Taylor got wasted at Steve's party last weekend.
2: I thought she was Mormon!
1: She's a jack mormon.
by JFLV November 16, 2004
1. A nominal, or non-practicing, Mormon.

2. A person born in a family with Mormon roots, but who does not live all the precepts of the faith.

3. A person not unfriendly to Mormons, or who might even believe some or all Mormon tenets, but who - while not being adversarial - does not participate in the sacraments of the faith, or abstain from proscribed actions (such as smoking, or drinking coffee, tea, or alcoholic drinks).

4. (Archaic) A person with many Mormon acquaintances and friends and/or who sympathizes with them and their beliefs, but chooses not to affiliate with the church.
"He's a jack Mormon, but if anyone's in trouble he's the first one there to help"

"She likes to go to Relief Society meetings, but she just can't give up her doubts about the Book of Mormon or her morning cup of coffee. She's a confirmed jack Mormon."
by Nonobvious October 22, 2009

1. A person who associates with The Latter Day saints but is not one of them

2. A Latter Day saint who does not practice or observer the customs and beliefs of The Latter Day Saints
He's the local Jack Mormon of the town.
by The Return Of Light Joker November 6, 2007
A person who claims to be a 'member' of the Church of Jesus Christ of Latter-Day Saints, but is mostly inactive. Observes some basic principles of 'mormonism', but generally has torn up the rule book. Usually to be found in Utah, where a high concentration of this sect can be found.
A Jack-Mormon often does not observe their guidance of not consuming alcohol or coffee. Can be found to attend the church for say a wedding or funeral. A Jack-Mormon usually, finds themselves at odds with the church. Often this person has been raised in a mormon family unit but come to the conclusion that it does not suit their beliefs.

From experience in Salt Lake City (HQ of Mormonism), this person(typical Jack-Mormon) cannot wait to escape the confines of Utah over the border to Nevada, often going to the small city of Wendover being the nearest to get to, to partake in prostitution, alcohol and gambling.
by tictactaylor February 11, 2010